This application claims priority based on German application 199 43 183.3, filed Sep. 9, 1999 and the contents thereof are incorporated herein by reference.
1. Field of the Invention
The present invention relates to methods for adjusting color in an image, more particularly, to adjusting color in an X-ray image.
2. Background Art
In the radioscopy of objects, sub-objects are represented by varying brightness levels in accordance with their X-ray absorption (grayscale image). In films, high-absorbing objects/sub-objects are represented as light images, while low-absorbing objects/sub-objects produce significant darkening and are therefore represented as darker images. In electronic image processing, using reverse imaging is also customary, i.e. light grayscale values are used for objects/sub-objects having weak X-ray absorption.
The objects/sub-objects may be X-rayed using varied energy levels to provide improved identification of the material(s) that the objects/sub-objects are made from. The type materials of the X-rayed objects or sub-objects may be determined from absorption values determinable at the different energy levels.
For visual determination of the objects'/sub-objects' materials, the materials of the objects/sub-objects may be represented by different colors. For example, a color is assigned to an average atomic number that defines a specific material type. This produces a so-called false-color-image for the human eye, made up of two specific types of information: absorption and material.
Accordingly, if two materials having identical absorption (brightness), but are made from different materials (color), are compared to this false-color-image, the two material appear to have different brightness levels to the human eye, since the human eye has different sensitivity to different colors. Therefore, a green object is perceived to be much brighter than a blue object. This results in the conclusion that the blue object is subject to a higher absorption than the green one, because the human eye is especially sensitive to green, and on the contrary, is insensitive to blue. This leads to unpleasant visual strain for a person viewing the image and to poor discernability of objects represented by darker colors. The latter is particularly important when analyzing an X-ray image, because here indeed is where superimposed sub-objects in the image must be discernable as shadings lying one behind another.
European patent documents EP 0 523 898 B1, EP 0 584 690 B1, and EP 0 758 514 B disclose devices and processes that improve color images in the television and video sector, taking into account the three primary colors—red, green, and blue—according to the NTSC (National Television System Committee) standard.